Glyoxalation of vinylamide polymer

ABSTRACT

The present invention is directed to a method for preparing a cellulose reactive adduct of polyvinylamide and a composition resulting from the method. The preparation of the cellulose reactive adduct is carried out close to a Critical Concentration defined herein. When the reaction is run close to this Critical Concentration, the risk of gelation is minimized, consumed glyoxal is maximized, and shelf live is enhanced. Additionally, the glyoxalated vinylamides of the present invention impart improved wet and dry strengthening efficiency to paper and paperboard when compared to adducts disclosed in previously described art.

This application claims the benefit of U.S. Provisional Application Nos.60/843,156, filed Sep. 7, 2006 and 60/851,188, filed Oct. 12, 2006herein incorporated entirely by reference.

FIELD OF THE INVENTION

The present invention is directed to a method for preparing a cellulosereactive adduct of polyvinylamide and a composition resulting from themethod.

The polyvinylamide cellulose reactive adduct obtained by the process ofthe invention is used as dry and wet strength aid for paper or board andmay be applied to cellulose in the wet end or applied directly to a wetweb paper or board.

BACKGROUND OF THE INVENTION

The use of synthetic water-soluble polymers as wet end additives for thestrengthening of paper and paperboard is widely practiced. The use ofcellulose reactive water-soluble vinylamide copolymers as paperstrengthening agents is also common. One particular class of vinylamidepolymer strength aids includes vinylamide polymers which are modifiedwith glyoxal or cellulose reactive agents in such a way as to bethermosetting.

U.S. Pat. No. 3,556,392 describes the synthesis of glyoxal-reactedwater-soluble vinylamide polymers used as paper strength agents. Thevinylamide polymers can contain ionic comonomers or other comonomerswhich impart specific functionalities to the polymers to improveaffinity to cellulose. The backbone vinylamide polymer is reacted withenough glyoxal to form a thermosetting adduct. The reaction is catalyzedby raising the pH of the reaction solution to approximately 8, and whena slight increase in solution viscosity is noted the pH is lowered toapproximately 7 to slow the progress of the reaction. When apredetermined viscosity target is reached, the reaction is quenched bylowering the pH to approximately 3.5 to 4. The degree offunctionalization of the vinylamide polymer with glyoxal is monitored bymeasuring the increase in viscosity of the reaction solution usingGardner-Holdt bubble viscometers. U.S. Pat. No. 3,556,392 teaches thatfollowing the final acid quench, when the desired extent of reaction hasbeen reached, approximately half of the original glyoxal remainsunreacted in the finished product and does not function as a strengthaid.

U.S. Pat. No. 3,556,392 teaches the prior art finished product will forman insoluble gel when aged for 8 days at 73° F. and at a concentrationof 9 percent solids.

U.S. Pat. No. 4,217,425 discloses a strength aid made from an aqueousblend of acrylamide homopolymer, polyDADMAC (polydiallyldimethylammonium chloride) and glyoxal. The reaction mixture is catalyzed byinvoking mildly alkaline conditions and the solution viscosity ismonitored until a predetermined increase in viscosity has been reached;at which time the reaction is “killed” by lowering the pH toapproximately 4. In example 1 from U.S. Pat. No. 4,217,425, acrylamidepolymer, DADMAC polymer and glyoxal are mixed in solution under alkalineconditions. After 360 minutes the solution viscosity is measured as 17cps, after 400 minutes the viscosity is 32 cps and after 415 minutes theviscosity is 55 cps. The increase in molecular weight is measured as anincrease in solution viscosity.

A paper strengthening agent made by glyoxalation of a cationicacrylamide polymer with a molecular weight in the range of 500 to 6000is taught by U.S. Pat. No. 4,605,702. This patent alleges improved lossof wet strength over time compared to previous disclosures. A viscometeris used to measure the increase in the solution viscosity as theglyoxalation reaction progresses.

A glyoxalated-polyvinylamide which is alleged to have enhanced storagestability resulting from multiple additions of glyoxal and the additionof an aldehyde scavenger is taught in U.S. Publication No. 20050187356.The backbone polymer is glyoxalated at a pH of 8 until the viscosityreaches 12 cps, at which time the reaction pH is lowered to 7.1 to 7.2.The reaction continues at a moderate rate until a viscosity of 54 cps isreached, at which time the reaction is quenched by addition of sulfuricacid to lower the pH to about 3.5.

PCT Published Application No. 2006/016906 describes a cationicvinylamide crosslinked polymer which is treated with a cellulosereactive agent such as glyoxal to impart strength to paper.

U.S. Pat. Nos. 4,954,538, 5,041,503 and 5,320,711 teach microparticlesof cross linkable, glyoxalated-polyvinylamide prepared by reverse phasemicroemulsion polymerization and describe adding glyoxal to the microemulsion polymer to form a glyoxalated polymer.

The methods and products described above have clear disadvantages. Theaqueous glyoxalated-polyvinylamide adduct formation described in theknown art is monitored by following the increase in solution viscosityas the reaction progresses. If the reaction is allowed to move forwardunimpeded, a water-insoluble gel will ultimately form. Glyoxalatedmicroemulsions (U.S. Pat. Nos. 4,954,538, 5,041,503 and 5,320,711)contain significant organic carrier oils which are costly and give highvolatile organic compounds (VOC). There are numerous applications wherehigh VOC amounts restrict use.

The various glyoxalated-polyvinylamide adducts commercially available atpresent are commonly known to have an approximate shelf-life range ofabout four to six weeks, depending on the pH, concentration of theadduct polymer solution and temperature at the time of storage.

When the desired extent of glyoxalation is reached, approximately halfof the original glyoxal remains unreacted in the finished product anddoes not function as a strength aid.

The inventor has discovered that unexpectedly, improved adducts areformed by the aqueous reaction of glyoxal and vinylamide polymer whenthe concentration of the vinylamide polymer during the reaction is closeto a Critical Concentration which determines an inflection point(s)defined below.

Furthermore, the adducts formed by the inventive method are not limitedby the constraints of poor storage stability, do not run the risk ofgelation, contain less unconsumed glyoxal than products of priorprocesses and contain essentially no oils. Additionally, the glyoxalatedvinylamides of the present invention impart improved wet and drystrengthening efficiency to paper and paperboard, when compared toadducts disclosed in previously described art.

SUMMARY OF THE INVENTION

The present invention relates to a novel method for preparingthermosetting cellulose reactive polyvinylamide adduct. Specifically theinvention encompasses:

a method for preparing a cellulose reactive functionalizedpolyvinylamide adduct comprising

-   -   reacting a substantially aqueous reaction mixture of a        vinylamide polymer and a cellulose reactive agent to form the        adduct.

The concentration of the vinylamide polymer for the above reactionmixture is defined variously as below:

the concentration of the vinylamide polymer is below, equal to or nomore than 1 percentage points (1%) above a Critical Concentration of thereaction mixture. At concentrations above the Critical Concentration,the viscosity of the reaction mixture increases with the forwardprogress of adduct formation, and at concentrations below the CriticalConcentration, the viscosity of the reaction mixture decreases with theforward progress of adduct formation.

For clarity, what is meant by about 1% of the reaction mixture above aCritical Concentration is for example, if the Critical Concentration is5 wt. %, then 1% above would mean 6 wt. %.

Secondly, the concentration of the vinylamide polymer may be defined asless than about 5 wt. % of the reaction mixture at any stage during thecatalyzed adduct reaction.

For example, the concentration of the vinylamide polymer may be definedas less than about 4 wt. % of the reaction mixture at 10, 20, 30, 40 or50% of completion of the glyoxalation reaction. For example, theconcentration of the vinylamide polymer may be approximately 10 wt. % atonset, then diluted to less than 4 wt. % at 10% completion of theglyoxalation reaction.

It is preferred that the concentration be less than about 4 wt. % at theonset of functionalization of the vinylamide polymer.

Thus a substantially aqueous glyoxalated-polyvinylamide thermosettingpolymer composition comprises a reaction product of a vinylamide polymerand glyoxal wherein the vinylamide polymer has an average molecularweight of at least about 30,000 to at least about 500,000 or even ashigh a molecular weight as 5,000,000. For example, the molecular weightmay be at least about 50,000, 70,000, 100,000 or higher. Generally, atleast 40 wt. % of the total glyoxal, and preferably more than 50% of theglyoxal has been consumed during the reaction and the reaction containssubstantially no organic liquid. The molar ratio of the amidefunctionality on the vinylamide polymer and glyoxal during the reactionis between 2 to 1 and 12 to 1, and the reaction is catalyzed to a pointwhere at least 40% of the cellulose reactive agent is consumed in thereaction. Preferably the molar ratio of vinylamide polymer to cellulosereactive agent is between 3 to 1 and 8 to 1, and at least 50% of thecellulose reactive agent is consumed in the catalyzed reaction.

Alternatively, the reaction mixture has a pre-reaction viscosity and asecond viscosity which is measured once the reaction has progressed to apoint where at least 50 wt. % of the total cellulose reactive agent hasbeen consumed, and the difference between the pre-reaction and secondviscosities is characterized by a viscosity decrease, no change inviscosity, or increase of less than about 50% of the pre-reactionviscosity. For example, if the pre-reaction viscosity (bulk viscosity)is 20 centipoise, the second viscosity will be no more than 30centipoise.

The invention further embodies

A method for increasing the wet or dry strength of paper or boardcomprising the steps of:

a) providing an aqueous slurry of cellulosic fibers;

b) adding the adduct obtained by the method according to the inventionto the aqueous slurry;

c) forming a web from the aqueous slurry formed in step b);

and

d) drying the web.

A method for increasing the wet or dry strength of paper or board mayalso be accomplished by means other than adding the adduct to thecellulosic slurry such as incorporation on the paper or board forexample, comprising the steps of:

a) spraying, coating or otherwise applying the adduct obtained accordingto method of the invention onto a wet web, paper or board;

and

b) drying the coated wet web, paper or board.

Compositional embodiments include:

a paper or board incorporating the adduct obtained by the methods above;

a glyoxylated-polyvinylamide thermosetting resin obtained by the methodsabove;

a substantially aqueous glyoxalated-polyvinylamide thermosetting polymercomposition comprising a reaction product of a vinylamide polymer andglyoxal wherein the vinylamide polymer has a weight average molecularweight (Mw) of at least 25,000, preferably at least 30,000, mostpreferably at least 70,000 and the amount of glyoxal consumed in thecatalyzed reaction is at least about 40 wt. %, and preferably more than50 wt. % of the total glyoxal charged. The amide to glyoxal molar ratiois in the range of 2:1 to 12:1, and preferably in the range of 2.5 to8:1. Further, the aqueous composition contains substantially no organicliquid.

DETAILED DESCRIPTION OF THE INVENTION Definition of Basic Terms

For the purposes of the invention, the reaction of the pendant amidegroups of vinylamide polymers with glyoxal will be referred to as a“glyoxalation reaction” or simply “glyoxalation”, in this application.The product of said glyoxalation reaction will be referred to asglyoxalated-polyvinylamide or glyoxalated-polyvinylamide adduct or justplain adduct(s).

The term “vinylamide polymer” refers to the starting polymer beforeglyoxalation. It may be a homopolymer, copolymer or terpolymer. Thestarting vinylamide polymer or formed vinylamide polymer adduct may becationic, potentially cationic, anionic, potentially anionic, nonionicor amphoteric. The starting vinylamide polymer may be a blend ofvinylamide polymer and another miscible non-vinylamide polymer.

A copolymer for purposes of the invention is a polymer formed from twoor more monomers.

The term “catalyzed glyoxalation reaction” refers to a glyoxalationreaction carried out in an environment such that physical or chemicalconditions cause the reaction to progress at a moderate to acceleratedrate, wherein the desired reaction is obtained in less than about 12hours, or more preferably in less than 6 hours, less than 3 hours oreven less than about 1 hour. Preferably the glyoxalation is effectedunder alkaline conditions or by addition of a base or basic buffer.

The term “substantially aqueous reaction mixture” for the purposes ofthe invention means that the adduct formation is carried outsubstantially in the absence of organic oils. For example, it is knownto glyoxalate a vinylamide polymer in an inverse micro-emulsion whichcomprises both an oil phase and a water phase. The oil phase comprisesat least one hydrocarbon. Typically the oil phase will be mineral oil,toluene, fuel oil, kerosene, odorless mineral spirits, or mixtures ofthe like. The weight of oil in these prior art processes often exceedsthe weight of polymer formed. Thus for the purposes of the invention,adduct formation is carried out in a “substantially aqueous reactionmixture” wherein the presence of organic oils does not exceed the weightof vinylamide polymer, preferably oil weight does not exceed 50 wt. % ofthe vinylamide polymer and most preferably there is no significantamount of oil present during the adduct formation. Substantially aqueousmeans oil makes up less than about 20 wt. % of the vinylamide polymerand preferably less than 10, or less than about 5 or less than about 1wt. %.

The wt. % of the vinylamide polymer is based on the total weight of thereaction mixture.

Wt. % Glyoxal consumed is based on total weight of glyoxal charged.

Molecular weight for purposes of the invention means weight averagemolecular weight (M_(w)).

Molecular weight is determined by standard methods such as GPC. Forexample, the average molecular weight may be determined by conventionalcalibration techniques using acetate buffer and the following columns:TSK PWXL (Guard+G6000+G3000). Polyethylene oxide and polyethylene glycolstandards may be used to calibrate the column set.

Other materials which are soluble or miscible in water may additionallybe present in the reaction mixture. Chelating agents, electrolytes suchas sodium chloride, surfactant and polar solvents such as methanol maybe present in the reaction mixture. Low molecular weight cationicpolymers may also be present in the reaction mixture, for examplepolysaccharides, polydiallyldimethylammonium chloride (polyDADMAC) andpolyamines. Inorganic cationic flocculants may also be present, such asferric chloride, aluminum sulfate, polyaluminum chloride and aluminumchlorohydrate, etc.

The vinylamide polymer or formed adduct may be further combined with asecond polymer (different than the vinylamide polymer) which may becationic, anionic, non-ionic or amphoteric. For example the glyoxalatedpolyvinylamide polymer may be combined with a polyamine orpolyaminopolyamide epichlorohydrin (PAE).

For example, the second polymer may be cationic and formed from cationicor potentially cationic monomers described herein. The second polymermay be a Mannich base, polyamine, polyethyleneimine,polyamidoamine/epichlorohydrins, polyamine epichlorohydrin products,dicyandiamide polymers including polyamine-dicyandiamide andpolydicyandiamide formaldehyde polymers, or cationic starch. Additionalexamples might be polyamine-epihalohydrin resins, such aspolyaminopolyamide-epihalohydrin resins which are also cationicthermosetting materials used to increase the wet strength of papers.

Vinylamide

The term vinylamide refers to any vinyl monomer containing an amidefunctionality including but not limited to acrylamide, methacrylamide,N-methyl acrylamide or any other substituted acrylamide.

Synthesis of Backbone Vinylamide Polymer

The backbone vinylamide polymers, which are subsequently glyoxalated bythe process of the invention, may be synthesized by free radical orredox catalysis polymerization of a vinylamide monomer, and optionallyone or more ionic comonomer(s) or nonionic comonomers. Cross-linkingagents with multiple polymerizable vinyl functionalities can also beincluded in the formulations to impart structure to the backbonepolymer. A chain transfer agent, such as sodium hypophosphite, may beused to control the molecular weight of the polymer molecules, as wellas to introduce branching.

The water soluble vinylamide polymer may be formed by any suitablepolymerisation process. The polymers may be prepared for instance as gelpolymers by solution polymerisation, water-in-oil suspensionpolymerisation or by water-in-oil emulsion polymerisation. The polymersmay be produced as beads by suspension polymerisation or as awater-in-oil emulsion or dispersion by water-in-oil emulsionpolymerisation, for example according to a process defined byEP-A-150933, EP-A-102760 or EP-A-126528.

Alternatively the water soluble polymer may be provided as a dispersionin an aqueous medium. This may for instance be a dispersion of polymerparticles of at least 20 microns in an aqueous medium containing anequilibrating agent as given in EP-A-170394. This may for example alsoinclude aqueous dispersions of polymer particles prepared by thepolymerisation of aqueous monomers in the presence of an aqueous mediumcontaining dissolved low intrinsic viscosity polymers such as polydiallyl dimethyl ammonium chloride and optionally other dissolvedmaterials for instance electrolyte and/or multi-hydroxy compounds e.g.polyalkylene glycols, as given in WO-A-9831749 or WO-A-9831748.

Molecular Weight, Structure and Composition of Vinylamide Polymer

The vinylamide polymers that are glyoxalated by the process of theinvention can be of any molecular weight obtainable by methods ofpolymer synthesis known to those skilled in the art. The vinylamidepolymer may be nonionic, cationic, anionic or amphoteric. The vinylamidepolymer may be crosslinked or structured.

The average molecular weight of the vinylamide polymer may range from500 to about 5,000,000 or even 10,000,000 Daltons.

The starting vinylamide polymer has an average molecular weight of atleast 500, but preferably at least about 10,000 to about 5,000,000. Forexample, 50,000 to 2,000,000, 70,000 to 1,000,000 are envisioned. Theprocess of the invention allows glyoxalation of vinylamide polymers ofabout 50,000 or greater, about 70,000 or greater and even about 85,000or 100,000 or greater. Preferable average molecular weight ranges arefor example between 5,000 to about 150,000, 10,000 to about 150,000 or25,000 to about 150,000.

Suitable vinylamide monomers are (meth)acrylamide, C₁₋₄ mono substituted(meth)acrylamides such as N-methyl(meth)acrylamide,N-ethyl(meth)acrylamide. The most preferred vinyl monomers areacrylamide and methacrylamide.

The term (meth)acrylamides includes both acrylamide and methacrylamide.

The vinylamide content of the polymers of the present invention providesthe sites to which the cellulose reactive agent or glyoxal substituentsare attached. The minimum proportion of vinylamide units which should bepresent should be sufficient so that the glyoxalated polymer isthermosetting, such that the glyoxalated polymer forms a water-insolublefilm when it is laid down from water solution on a glass plate andheated for 5 minutes at about 105° C.

Thus the vinylamide polymer (before glyoxalation) should be formed fromat least about 10 wt. % vinylamide monomers. Preferably, the vinylamidepolymer is formed from at least about 20 to about 100 wt. % vinylamidemonomers. For example, the vinylamide polymer is at least formed fromabout 20 to about 99 wt %, at least about 25 to about 90 wt. %vinylamide monomers, or at least about 50 wt. % and most preferably atleast about 70 wt % vinylamide monomers. The wt. % is based on theweight of the total weight of monomers charged to form the vinylamidepolymer.

Once the monomers polymerize, they become incorporated units in thepolymer.

Thus there may be units in the polymers of the present invention whichmay confer ionic properties upon the polymer, or those which act asdiluents or spacers, or which confer special properties, for example,improved or diminished water-solubility.

Ionic comonomers, which can be used in conjunction with vinylamidemonomers, can be cationic, potentially cationic, anionic, potentiallyanionic or amphoteric. When using cationic comonomers, one or morecationic monomers can be used, and the total amount of cationic monomershould be such that a glyoxal adduct of the vinylamide copolymer isself-substantive to cellulose fibers in aqueous suspension.

Cationic comonomers are especially preferred as the cationic chargegives substantivity to cellulose fiber.

Suitable cationic monomers or potentially cationic monomers includediallyldialkyl amines, 2-vinylpyridine,2-(dialkylamino)alkyl(meth)acrylates, dialkylamino alkyl(meth)acrylamides, including acid addition and quaternary ammonium saltsthereof. Specific examples of such cationic monomers or potentiallycationic monomers are diallyldimethyl ammonium chloride,(meth)acryloyloxy ethyl trimethylammonium chloride (dimethyl aminoethyl(meth)acrylate, methyl chloride quaternary salt),2-vinyl-N-methylpyridinium chloride, (p-vinylphenyl)-trimethylammoniumchloride, (meth)acrylate 2-ethyltrimethylammonium chloride,1-methacryloyl-4-methyl piperazine, Mannich poly acrylamides i.e.polyacrylamide reacted with dimethyl amine formaldehyde adduct to givethe N-(dimethyl amino methyl) and (meth)acrylamido propyltrimethylammonium chloride.

Potentially cationic monomers may be for example monomers that give acationic charge under acidic conditions such as when an aminefunctionality on the potentially cationic monomer is protonated.

The amount of cationic comonomer may range from about 0% to about 90 wt.%, about 0.1 to about 50 wt %, about 0.1 to about 40, about 0.1 to about30, about 0.1 to about 25 wt % or about 0.1 to about 15 or about 10 wt.percent. The wt. % is based on the total weight of monomer(s) charged toform the vinylamide polymer.

Furthermore, the vinylamide monomers may be copolymerized with vinyltertiary amines such as dimethylaminoethyl acrylate or vinylpyridine.The tertiary amine groups can then be converted into quaternary ammoniumgroups by reaction with methyl chloride, dimethyl sulfate, or benzylchloride to produce a cationic polymer. Moreover, polyacrylamide can berendered partially cationic by reaction with glycidyl dimethyl ammoniumchloride.

Suitable anionic monomers may be selected from vinyl acidic materialsuch as acrylic acid, methacrylic acid, maleic acid, allyl sulfonicacid, vinyl sulfonic acid, itaconic acid, fumaric acid, potentiallyanionic monomers such as maleic anhydride and itaconic anhydride andtheir alkali metal and ammonium salts,2-acrylamido-2-methyl-propanesulfonic acid and its salts, sodium styrenesulfonate and the like. Alternatively, if the starting vinylamidepolymer is polyacrylamide, it may be partially hydrolysed to achievesome anionic character then functionalized with the cellulose reactiveagent.

Potentially anionic monomers may be for example acrylamide, which whenpartially hydrolysed forms an acid which may give anionic character tothe polymer under basic conditions. Alternatively, the potentiallyanionic monomers may be for instance an anhydride monomer, such asmaleic anhydride or itaconic anhydride, which can be hydrolysed to formthe corresponding acid.

As stated above, the vinylamide polymer may be amphoteric; that is thepolymer may include anionic and cationic functionality. The amphotericvinylamide polymer may be formed from both anionic and cationic monomersor alternatively from zwitterionic monomers. The various monomers(anionic, cationic and/or zwitterionic) may be reacted in any wt. ratioto form the amphoteric vinylamide polymer. It is preferable that thepredominate charge on the formed amphoteric vinylamide polymer becationic. Thus, the mole % of cationic monomer dominates over the mole %anionic monomer incorporated into the amphoteric vinylamide polymer.

Suitable non-ionic monomers other than the vinylamide may be selectedfrom the group consisting of (meth) acrylic esters such asoctadecyl(meth)acrylate, ethyl acrylate, butyl acrylate,methylmethacrylate, hydroxyethyl(meth)acrylate and 2-ethylhexylacrylate;N-alkyl acrylamides, N-octyl(meth)acrylamide, N-tert-butyl acrylamide,N-vinylpyrrolidone, N,N-dialkyl(meth)acrylamides such as N,N′-dimethylacrylamide; styrene, vinyl acetate, hydroxy alkyl acrylates andmethacrylate such as 2-hydroxy ethyl acrylate and acrylonitrile.

The starting vinylamide polymer or formed vinylamide polymer adduct maybe crosslinked, branched or otherwise structured or linear. For example,the starting vinylamide polymer or formed vinylamide polymer adduct maybe linear, crosslinked, chain-transferred, or crosslinked &chain-transferred (structured).

Cross linking agents are usually polyethylenically unsaturatedcrosslinking agents. Examples are methylene bis(meth)acrylamide,triallylammonium chloride; tetraallyl ammonium chloride,polyethyleneglycol diacrylate; polyethyleneglycol dimethacrylate;N-vinyl acrylamide; divinylbenzene; tetra(ethyleneglycol) diacrylate;dimethylallylaminoethylacrylate ammonium chloride; diallyloxyaceticacid, Na salt; diallyloctylamide; trimethyllpropane ethoxylatetriacryalte; N-allylacrylamide N-methylallylacrylamide, pentaerythritoltriacrylate and combinations thereof. Other systems for crosslinking canbe used instead of or in addition to this. For instance covalentcrosslinking through pendant groups can be achieved, for instance by theuse of ethylenically unsaturated epoxy or silane monomers, or by the useof polyfunctional crosslinking agents such as silanes, epoxies,polyvalent metal compounds or other known crosslinking systems.

Chain transfer agents may be used to synthesize the starting vinylamidepolymer. Suitable chain transfer agents are 2-mercaptoethanol; lowmolecular weight organic acids such as lactic acid, formic acid, malicacid or butyric acid; isopropyl alcohol; thioacids and hypophosphites.

Cellulose Reactive Agent

The cellulose reactive agent will comprise more than one aldehydefunctionality.

The cellulose reactive reagents are selected from the group consistingof glyoxal, glutaraldehyde, furan dialdehyde, 2-hyroxyadipaldehyde,succinaldehyde, dialdehyde starch, diepoxy compounds, and combinationsthereof.

Glyoxal is the preferred cellulose reactive reagent.

The molar ratio of amide (on the vinylamide polymer) to cellulosereactive agent will vary from about 12:1 to about 2:1, for example,about 10:1 to about 2.5:1, about 6:1 to about 2.5:1 and about 6:1 toabout 3:1.

The molar content of amide on the vinylamide polymer may be determinedexperimentally by methods well known in the art or calculated from theknown monomer composition.

Reaction Conditions

Base Addition

Base addition or changing the pH to above 7 is the most common method ofcatalyzing the glyoxalation reaction. Preferably, a pH range of 7 to 13is generally considered to be a catalytic environment for the reaction.For example, a pH range of 8 to 12 is especially appropriate.

Alternatively, a concentrated pH buffer solution may be added tomaintain pH.

Concentration of the Vinylamide Polymer

For purposes of the invention, the concentration of vinylamide polymerrefers to the polymeric vinylamide before reaction with the cellulosereactive agent or before glyoxalation.

The vinylamide polymer may be formed before glyoxalation.

The process of this invention has been developed to incorporate and takeadvantage of unexpected rheological behavior observed in vinylamideglyoxalation reactions when the vinylamide polymer concentrations of thecatalyzed reaction mixtures are within particular ranges. One importantadvantage stemming from the process of the invention is that cellulosereactive adducts can be formed from starting vinylamide polymers ofsignificantly higher Mw than those enabled by the processes for makingcellulose reactive adducts disclosed in the prior art.

Moreover, a Critical Concentration exists for any given vinylamidepolymer, and the Critical Concentration of a vinylamide polymercoincides with an inflection point in the rheological behavior of asolution of that vinylamide polymer during the glyoxalation reaction.This rheological inflection point can be defined as the point on a plotof vinylamide polymer concentration versus change in reaction mixtureviscosity resulting from glyoxalation. The inflection point, andtherefore the Critical Concentration, is the theoretical point at whichthe slope of the plot line reverses direction.

The Critical Concentration for glyoxalation of a particular vinylamidepolymer is determined through empirical studies involving glyoxalationof the vinylamide polymer. Multiple glyoxalations of the vinylamidepolymer should be carried out in a number of independent reactionsolutions, wherein each solution has a known and different vinylamidepolymer concentration which is expressed as a wt. % of the totalreaction mixture. The rheological behavior or change in viscosity of areaction mixture is measured as the glyoxalation reaction proceeds, andthis change in viscosity can be either a continued increase in viscosityor a continued decrease in viscosity as the reaction proceeds, or evenno significant change in viscosity as the reaction proceeds. If theviscosity trend increases as the reaction proceeds, then theconcentration of vinylamide polymer in the reaction mixture is said tobe above the Critical Concentration for that vinylamide polymer. If theviscosity trend decreases as the reaction proceeds, then theconcentration of the vinylamide polymer in the reaction mixture is belowthe Critical Concentration for that vinylamide polymer. If nosignificant change in viscosity is measured as the reaction proceeds,then the concentration of vinylamide polymer in the reaction solution isat or very near the Critical Concentration of that vinylamide polymer.

When attempting to ascertain an empirically derived value of theCritical Concentration of a particular vinylamide polymer, it is helpfulfor an experimenter to understand that the magnitude of the viscositychange versus reaction extent of various reaction mixtures decrease asthe actual vinylamide polymer concentrations become more proximate tothe theoretical Critical Concentration for that particular vinylamidepolymer.

The Critical Concentration of a particular vinylamide polymer isstrongly influenced by the vinylamide polymer molecular weight, and istherefore specific for vinylamide polymers with specific molecularweights, and with other equivalent characteristics. Other factorsincluding but not limited to cross-linking, branching or otherstructuring, monomer composition, polymer ionicity and reaction solutionionic strength also affect the Critical Concentration. However,molecular weight has by far the most profound impact on the value of theCritical Concentration. When considering a specific vinylamide polymercomposition with all variables held constant except for molecularweight, the plot of the reaction mixture vinylamide polymerconcentration versus molecular weight depicts an inversely proportionalrelationship between molecular weight and Critical Concentration. As themolecular weight of vinylamide polymers is increased, the value of theCritical Concentration decreases.

The Critical Concentration can therefore vary considerably betweenvinylamide polymers of differing average molecular weights. For example,the Critical Concentration may vary from 0.2% to about 4.5 wt. % of thevinylamide polymer, about 0.3 wt. % to less than 4.0 wt. %, about 0.5 toabout 3.5 or 1.0 to about 3.0 or about 1.5 to about 2.5 wt. % of thevinylamide polymer. Vinylamide polymers with the highest efficiency fordeveloping strength in paper have been found to have CriticalConcentrations in the range of about 1.0% to about 3.0%.

As an example of how the Critical Concentration varies with the weightaverage molecular weight of vinylamide polymers, and consideringspecific vinylamide polymers composed of 90 weight percent acrylamideand 10 weight percent diallyldimethylammonium chloride (DADMAC), andwith no compounds present in the reaction mixture other than thevinylamide polymer, glyoxal, deionized water and a catalytic quantity ofsodium hydroxide; a polymer with a Mw of approximately 4,000,000 has aCritical Concentration of about 0.35 wt. % of the reaction mixture, anda polymer with a Mw of approximately 13,000 has a Critical Concentrationof about 3.5 wt. % of the reaction mixture.

Compositional and process related advantages have been found whenoperating glyoxalation processes at or below the Critical Concentration.It is also possible to realize the advantages of the process when thevinylamide polymer concentration is slightly above the CriticalConcentration. For example, the concentration can be about 1 percentagepoints above the Critical Concentration and the glyoxyalatedpolyvinylamides adduct produced will benefit from more efficientconsumption of the glyoxal reactant and better performance on paper,when compared to those adducts produced at higher concentrations knownpreviously (typically 8 to 12 wt. %).

One of the advantages of the process of the invention is the ability toglyoxalate relatively high average molecular weight vinylamide polymerwithout premature gelling of the glyoxalated adduct. For example, mostof literature exemplifies glyoxalation reactions wherein the startingvinylamide polymer has an average molecular weight ranging from 5,000 toabout 10,000 at concentrations of vinylamide polymer that range from 8to 12 wt. %. At these concentrations (8-12) the glyoxalation reaction ofa relatively high molecular weight of the starting vinylamide polymer(=>25,000) will prematurely gel causing incomplete glyoxalation of thestarting polymer and generating an insoluble gel. By using the processof the invention, a means is now available to glyoxalate a relativelyhigh molecular weight (=>25,000) starting polyvinylamide which in turngives better performance on paper or board.

Subjecting various samples of glyoxalated polyacrylamide to conditionsthat break aldehyde-amide bonds allows one to determine the Mw of thestarting or “backbone” polymer. This can be done by subjecting theglyoxalated vinylamide polymer to basic conditions for a period of time.

Within the scope of the invention, the concentration of the vinylamidepolymer can vary considerably, for example less than 4 wt. %, about 0.1to less than 4, less than 3.5, 0.5 to about 3.5 wt. % of the vinylamidepolymer, about 1.0 to about 3.5 or 1.0 to about 3.0 or about 1.5 toabout 3.0 wt. % of the vinylamide polymer.

Furthermore, it has been discovered that the Critical Concentration ofthe vinylamide polymer is generally at or less than 5.0 weight percentthe vinylamide polymer based on the total weight of glyoxalationreaction solution when the molecular weight is above 2000.

Further examples will illustrate the relationship between the CriticalConcentration of vinylamide polymer vs. weight average molecular weight.

A vinylamide polymer of molecular weight ranging from about 1,000,000 toabout 4,000,000 will give show a Critical Concentration which will varyfrom 1.0 to about 0.2 wt. %; a molecular weight ranging from about25,000 to about 175,000 will show a Critical Concentration which willvary from about 2.5 to about 1.1 wt. %; and a molecular weight rangingfrom about 2,000 to about 15,000 will vary from about 5.0 to about 3.5wt. %.

Percent Glyoxal Consumed

Prior processes which are run in substantially aqueous environments havenot been able to achieve efficient use of the glyoxal reactant, andtypically consume only about 50 wt. % of the total glyoxal charged.

The glyoxal consumed is determined by measuring the residual glyoxal(unbound glyoxal) remaining in the glyoxalation reaction mixture. Thereaction is continued until at least about 50 wt. % of the total glyoxalhas been consumed, and the reaction may also be usefully continued untilas much as 90 or more weight % of the total glyoxal is consumed in thereaction. The method of analysis is described in the Examples section.

Furthermore, a procedure for determining the amount of bound glyoxal inthe glyoxalated vinylamide polymer adduct is described in AnalyticalBiochemistry, Vol. 81, pp. 47-56.

Glyoxal consumption is at least about 40 wt. % or even at least 60, 65,75, 85 or 90 wt. % of the reactant glyoxal during the catalyzed reactionevent.

Reactant glyoxal is the amount of total glyoxal charged before, duringor after the catalyzed reaction.

Glyoxal may be charged in any number of increments before or during thereaction.

Monitoring of Adduct Formation

In prior art processes, adduct formation between vinylamide polymer andglyoxal is monitored by measuring the viscosity of the reaction overtime. Once a certain increase in viscosity is achieved for a particularvinylamide polymer, the reaction is quenched by dilution and/or additionof acid.

However, the process according to the present invention shows only avery moderate increase in viscosity, a slight decrease in viscosity, orno increase at all. The inventor has observed that as the glyoxalationof the vinylamide polymer proceeds during the method of the invention,the turbidity of the reaction solution increases. Thus the presentmethod of the invention may follow the glyoxalation reaction with aturbidimeter or a viscometer.

Therefore, adduct formation may be determined by measuring the change inturbidity or viscosity of the aqueous reaction at the start of thereaction or T₀ and at a predetermined endpoint T_(e) (T_(e)−T₀).

The predetermined endpoint is for example, a desired increase inturbidity (measure of glyoxalation) for a particular vinylamide polymer.Thus, for example, a vinylamide polymer of 100,000 average molecularweight may give a turbidity of 0 to 5 NTU (nephelometric units) at thebeginning of the reaction (T₀) and a turbidity change of between 2 to1000 NTU at the predetermined endpoint. Once the turbidity of thereaction mixture has increase by about 2 to 1000 NTUs the reaction canbe quenched to prevent further reaction.

Turbidity measurements are especially important when the reaction takesplace at or below the Critical Concentration.

Viscometers and turbidimeters are well known in the art. For exampleSURFACE SCATTER 7SC turbidimeter is a continuous-monitoring instrumentdesigned for measuring turbidity in fluids. The instrument design isbased on the nephelometric principle, where light scattered by particlessuspended in the fluid is measured to determine the relative amount ofparticulate matter in the fluid.

In processes of the invention where a viscosity change occurs, (increaseor decrease) the extent of reaction may be monitored by the change inviscosity.

Viscosity is typically measured during the reaction using the UL adapterfor a BROOKFIELD LV series viscometer. The UL adapter has no spindlenumber. Only one setting is possible. The base of the adapter cup isremoved and the assembly is placed directly into the reaction mixture.Viscosity measurements are automatically recorded every second duringthe length of the catalyzed reaction. The viscometer is set to a speedof 60 rpm and the temperature of the reaction mixture is maintained at25° C.

Batch or Continuous Mode

The cellulose reactive polyvinylamide polymers may be synthesized in abatch or continuous mode. The process of the invention is particularlyfavorable for implementation in a continuous reactor with pH measurementcapability at the papermaking site.

The continuous reactor may be a tubular reactor.

Other variables which affect the rate of glyoxalation include, but arenot limited to, pH, temperature, vinylamide polymer molecular weight,reaction mixture concentration, molar ratio between vinylamide polymerand glyoxal, molar amide constituency of the vinylamide polymer, and thepresence of substances which interfere with the reaction.

The reaction is normally run at ambient temperatures. However thereaction may be carried out by the process of the invention over a widetemperature range.

The length of the reaction will vary depending on concentration,temperature and pH, as well as other factors.

Other conventional additives which may be added to the glyoxalationreaction are chelating agents to remove polymerization inhibitors, pHadjusters, initiators, buffers, surfactants and other conventionaladditives.

Application of Vinylamide Polymer Adduct

The polymers made by the process of the invention may be used in themanufacture of paper as dilute aqueous solutions. The aqueous solutionscan be applied to preformed paper by the tub or impregnation method, orby adding the solutions directly to paper-making fibrous suspensions atany point in the paper-making process where wet- and dry-strength resinsare ordinarily applied.

The cellulose reactive polyvinylamide adducts of the invention may beapplied or incorporated in the wet-end of the papermaking process orapplied to the wet paper.

The glyoxalated adduct may be added in the thick or thin stock. Whenadded to the thin stock it may be added before the fan pump.

A substantial amount of wet- or dry-strength is imparted when as littleas about 0.05 wt. % of the glyoxalated polyvinylamide, based on dryfiber weight of the furnish is added to the furnish.

For example, dosages of about 0.1 to about 20 (0.05-10 kg/metric ton)pounds dry polymer per ton of dry furnish, about 1 to about 12, (0.5-6kg/metric ton) about 1 to about 9 (0.5-4.5 kg/metric ton), about 1 toabout 8 (0.5-4 kg/metric ton) pounds dry polymer per ton of dry furnishis envisioned. More typically ranges of 1.5 to about 6 (1.0-3 kg/metricton) pounds dry polymer per ton of dry furnish are envisioned.

Application of the adduct to wet paper or board may be accomplished byany conventional means. Examples include but are not limited to sizepress, padding, spraying, immersing, printing or curtain coating.

The polymers of the invention are absorbed by the paper-making fibers atpH values ranging from about 3.5 to about 8.

The following examples describe certain embodiments of this invention,but the invention is not limited thereto.

EXAMPLES Determination of the Critical Concentration for Polyvinylamidesof Varying Mw

A set of seven compositionally equivalent vinylamide polymers aresynthesized with varying weight average molecular weights. The sevenpolymers are all copolymers of 90 weight percent acrylamide and 10weight percent DADMAC. The weight average molecular weights of theseseven polymers are shown in the table below.

Samples A, B, C and D are synthesized by heterogeneous suspensionpolymerization, and samples E, F and G are synthesized by aqueoussolution polymerization.

Average molecular weight is determined for samples A and B using a DAWNmulti-angle light scattering detector in combination with a differentialrefractive index detector. In the light scattering experiment, theamount of light scattered at a given angle is directly proportional tothe weight average molar mass and the concentration. A second order Zimmplot is used to generate molar mass data with a dn/dc (specificrefractive index increment) value of 0.1800 (angles 4-15).

For samples C thru G the average molecular weight is determined byconventional calibration techniques using acetate buffer and thefollowing columns: TSK PWXL (Guard+G6000+G3000). Polyethylene oxide andpolyethylene glycol standards are used to calibrate the column set.

TABLE 1 Vinylamide Polymer Mw Sample A B C D E F G Mw 3.93 MM 1.36 MM585 M 331 M 140 M 64 M 13 MGlyoxalation at Different Concentrations to Determine CriticalConcentration

Three separate aqueous reaction mixtures of each of the three vinylamidepolymers, “B”, “E” and “G” are made at concentrations in close proximityto the anticipated Critical Concentration for each of the polymers.Enough glyoxal is added to each of the nine polymer solutions such thata 4:1 amide:glyoxal molar ratio is established for each. For eachpolymer solution, 5 wt. % aqueous solution of sodium hydroxide is addeddropwise and continued until the pH of the solution reaches 9.2. Smalladditions of sodium hydroxide are administered as needed to maintain anearly constant pH of 9.2 for 30 minutes. At 5 minute intervals duringthe 30 minute reaction time, including time zero, 20 ml samples arecollected from the reaction beakers and immediately quenched by loweringthe pH to 4.0 with dilute sulfuric acid. In all, seven samples arecollected for each polymer reaction mixture. The viscosity of the sevensamples from each reaction mixture is measured using a Type 2 SCHOTTsuspended level viscometer, and is reported in centistokes.

In the case of all three polymers the results in Table 2 show that theCritical Concentration lies between two of the three testedconcentrations.

TABLE 2 Sample B Sample E Sample G Sample # 0.60% 0.80% 1.60% 1.25%1.50% 1.75% 3.2% 3.6% 4.0% 1 3.25 5.12 Gelled* 2.11 2.30 2.65 1.75 1.811.94 2 2.67 5.10 — 2.11 2.25 2.72 1.75 1.84 2.14 3 2.62 5.22 — 2.04 2.232.81 1.73 1.85 2.17 4 2.60 5.28 — 1.98 2.22 2.93 1.71 1.87 2.23 5 2.565.34 — 1.87 2.19 3.05 1.70 1.87 2.31 6 2.43 5.81 — 1.81 2.19 3.17 1.691.87 2.32 7 2.35 6.58 — 1.74 2.16 3.26 1.67 1.88 2.38 *At aconcentration of 1.6% the reaction mixture of Sample B gels before asample can be collected and quenched.

The Critical Concentration for:

Sample B lies between 0.6 and 0.8%;

Sample E lies between 1.50 and 1.75%;

Sample G lies between 3.20 and 3.6% vinylamide polymer concentrationbased on the total weight of the reaction mixture.

Samples of the glyoxalated vinylamide polymers “B”, “E” and “G”, whichare glyoxalated by the above described process of the invention, ataqueous vinylamide polymer concentrations of 0.6%, 1.25% and 3.2% (allbelow the Critical Concentration) respectively, are tested for drystrengthening efficiency. A commercially availableglyoxalated-polyvinylamide product is included in the analysis as areference point. The results in Table 3 show the dry strengtheningefficiency of each adduct when added at a rate of 6 dry pounds of adductper dry ton of paper (3 kg/metric ton).

The cellulose substrate used for the testing is obtained from alinerboard machine with a 100% post-consumer stock stream. Handsheets of140 grams per square meter weight are prepared for this testing.

TABLE 3 Tensile Strength Results Adduct of Adduct of Adduct ofCommercial Additive None “B” “E” “G” Product* Load in Kg 8.55 8.59 9.349.14 8.99 *The Commercial Product has a Mw of approximately 10,000 and aglyoxal to amide molar ratio of about 1 to about 2.5.

Comparison Examples

The glyoxalation procedure of example 1 from U.S. Pat. No. 3,556,932 isfollowed. The vinylamide polymer is a Mw of 10,000. The backbone polymeris 91 wt. % acrylamide and 9 wt. % diallyldimethylammonium chloride. Asample labeled as “1” is removed from the reaction mixture after theviscosity reaches a level of “C” (a Gardner-Holdt viscosity of C as an11% by weight solution at 30° C. on the bubble viscometer scale, and thepH of the sample is lowered to 3.5 to quench the reaction. The reactionmixture is allowed to react further until gellation occurred. A sampleof the gelled material, labeled as “2” is processed in a lab blender toliquefy the sample, and the sample is quenched to a pH of 3.5. Thesample labeled as “1” is considered a sample made by prior arttechnology, and the sample labeled as “2” is considered the absolutelimit of practical glyoxal reaction achievable by the prior arttechnique, as this sample has reached the gellation point.

The glyoxalation process of the invention is run at a concentration of2.0% solids on the same backbone polymer used in the comparison exampleabove.

From the inventive glyoxalation process, a sample labeled as “3” iscollected and quenched to a pH of 3.5, after having reacted to aturbidity level of 25 NTUs.

NTU units are determined using HACH 2100P turbidimeter.

Determination of Percent Glyoxal Consumed

All samples are adjusted to 2.0% concentration before analysis forresidual glyoxal, and based on this 2% solids each sample “1”, “2” and“3” contain an equivalent quantity of glyoxal before onset of theglyoxalation reaction.

The commercially available glyoxalated polyvinylamide is included withthe other samples for analysis of residual glyoxal. As this is acommercial sample, the inventors do not know the actual amount ofglyoxal added to this product prior to the glyoxalation reaction. Thusno % glyoxal reacted can be determined.

Percent residual glyoxal is determined from 2 wt. % aqueous solutions ofthe glyoxalated polyvinylamides. Residual glyoxal is removed from theglyoxalated polymer by dialysis through a 3500 MWCO membrane tubing. Tenmls of dialyzed sample is derivatized by adding 2.0 ml of o-(2,3,4,5,6Pentafluorobenzyl)-hydroxyamine hydrochloride (6.6 mgs/ml) forapproximately 2 hours. The glyoxal is then extracted from the dialysissolution using 1:1 hexane-diethyl ether. Analysis of the extract iscompleted by gas chromatography on an HP 5890 GC #6 instrument using aDB 5 15 M 0.53 mm i.d 1.5 um df column. Once the residual glyoxal isdetermined and the amount of pre-reaction glyoxal is known, the percentglyoxal consumed may be calculated as below in Table 4.

TABLE 4 Sample Residual Glyoxal Pre_Reaction Percent Reactant LabelDetected (Wt. %) Glyoxal (Wt. %) Glyoxal Consumed “1” 0.176 0.31 43.2%“2” 0.203 0.31 34.5% “3” 0.059 0.31 81.0% Commercial 0.362 UnknownUnknown Sample

Sample “3” shows almost double the weight percent of glyoxal consumed asin sample “1”.

The results in Table 5 show the dry strengthening efficiency of adducts“1” and “3” when added at a rate of 6 dry pounds of adduct per dry tonof paper (3 kg/metric ton). The cellulose substrate used for the testingis obtained from a linerboard machine with a 100% post-consumer stockstream. Handsheets of 140 grams per square meter weight were preparedfor this testing.

TABLE 5 Tensile Strength Results Additive None Adduct of “1” Adduct of“3” Load in Kg 8.55 8.98 9.18Paper Machine Trial Comparisons

Example 1

A vinylamide polymer of Mw 100,000 formed from acrylamide anddiallydimethylammonium chloride in a 90/10 weight ratio is glyoxalatedaccording to the invention. The glyoxalation reaction is run at 2 wt. %solids with the vinylamide polymer concentration at approximately 1.7wt. %. The amide:glyoxal molar ratio for the glyoxalation reaction is4:1. The starting viscosity before glyoxalation is 4.05 cps Theviscosity after glyoxalation is 4.75 cps The reaction is followed bymonitoring turbidity. The starting turbidity is 4.4 NTU and finalturbidity is 13.1 NTU.

Example 2

Example 2 is a glyoxalated polyvinylamide sold under the nameBAYSTRENGTH 3000.

To demonstrate the effectiveness of the glyoxalated product produced bythe process of the invention (example 5) with respect to known glyoxatedvinylamide polymer (example 6), both products are applied as drystrength agents to the paper furnish and resulting properties of thepaper examined in Table 6 below.

Paper is produced on a 2-ply fourdrinier with Bellbond (15% top ply: 85%bottom ply) at 2100 ft/min reel speed. The furnish is 80% virgin Kraftfiber and 20% OCC, 1% solids, a furnish charge of −350 milliequivalentsper liter, a conductivity of 3000 microSeimens and a pH in the head-boxof 5.1.

A glyoxalated vinylamide polymer formed by the process of the invention(example 1) and a conventionally glyoxalted vinylamide polymer (example2 comparison) are separately added to the furnish in the thin stockbefore the fan pump. The glyoxalated adduct samples are applied at 1lb/ton and 3 lb/ton for each (based on dry weight of furnish). Resultingpaper is characterized by tensile strength, Ring crush, Concorameasurements and Compression STFI.

Example 1 is a glyoxalated polyvinyl amide. The base polyvinyl amidebefore glyoxalation is ˜100,000 average molecular weight and is formedfrom a 90/10 (wt. % based on total polymer weight) of acrylamide anddiallydimethylammonium chloride.

The results in Table 6 compare paper properties using the product of theinvention (example 1) and a known product (example 2).

TABLE 6 Ring Crush¹ MD Tensile² STFI³ Concora⁴ Blank 1.173 1.247 37.5691.592 Dosage Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 1 Ex. 2 1 lb/ton*1.246 1.209 1.379 1.331 39.611 38.501 1.756 1.679 3 lb/ton* 1.266 1.2541.384 1.377 38.319 38.304 1.895 1.732 ¹Ring Crush is determined using aMESSMER BÜCHEL CRUSH TESTER model K440 according to TAPPI T 822 method.Ring crush is a physical test of the paper's strength. (Higher isbetter) ²MD Tensil is determined using an INSTRON Model 5565 accordingto PATPAC D34 method. ³Compression STFI is determined using aMESSMER-BÜCHEL Model K455, according to TAPPI T 826 method. ⁴Concora isdetermined using a Medium Fluter Model No. JKB according to TAPPI T 809.

The product produced by the process of the invention gives moreefficient gyoxalated polyacrylamide useage.

Example 3 Laboratory Technique for Determining Starting Molecular Weightof the Polyvinylamide Polymer

The following experiment is aimed at subjecting various samples ofglyoxalated polyacrylamide to conditions that break aldehyde-amide bondsand yield a polymer with the same Mw as the starting or “backbone”polymer.

A 91% acrylamide/9% DADMAC polymer (labeled as Sample A) of Mw=100,561is used to form a glyoxalated adduct by the process of the invention.The polymer is diluted with water and glyoxal such that a 4 to 1 amideto glyoxal molar ratio is achieved, and the total solids of the reactionmixture is 2.0% The reaction is catalyzed by the addition of dilutesodium hydroxide to raise the solution pH to 9.5. The turbidity of thereaction solution is monitored, and after a net increase in turbidity of50 NTU is achieved the reaction is quenched by the addition of enoughsulfuric acid to lower the solution pH to 3.5. This formed adduct islabeled as Sample B.

To Sample B, enough dilute sodium hydroxide is added to raise the pH ofthe solution to 12.6, and the pH is maintained at this level for 30minutes. After 30 minutes, the pH is returned to 3.5 by addition ofdilute sulfuric acid, and this solution is labeled as Sample C. TABLE 7give the Mw determinations for samples A thru C.

TABLE 7 Sample A B C Mw* 100,578 298,269 100,661 *Determined by standardGPC methods.

The results for Samples A, B and C above indicate that maintaining thepH of a glyoxalated adduct at 12.6 for 30 minutes causes the Mw of theadduct to revert back to that of the starting polymer prior to adductformation.

A sample of glyoxalated polyacrylamide manufactured by a prior artprocess, and sold under the trade name of Raisabond Plus 7118, islabeled as Sample D. A portion of Sample D is mixed with water to form asolution with 2% solids. Dilute sodium hydroxide is added to thesolution to increase the pH to 12.6. The pH is maintained at 12.6 for 30minutes, after which the pH is lowered to 3.5 by the addition of dilutesulfuric acid. This solution is labeled as Sample E.

TABLE 8 Sample D E Mw* 347,937 10,503 *Determined by standard GPCmethods.

The results for samples D and E indicate that the starting polymer Mw ofRaisabond Plus 7118 is approximately 10,000.

1. A method for preparing a cellulose reactive functionalizedpolyvinylamide adduct comprising reacting a substantially aqueousreaction mixture of a vinylamide polymer and a cellulose reactive agentto form the adduct, wherein the concentration of the vinylamide polymeris below, equal to or no more than 1% above a Critical Concentration andthe Critical Concentration is defined as the concentration of thevinylamide polymer above which Critical Concentration the viscosityincreases for the reaction mixture resulting from the forward progressof the adduct formation, and below which Critical Concentration, theviscosity decreases for the reaction mixture resulting from the forwardprogress of adduct formation, wherein the cellulose reactivefunctionalized polyvinylamide adduct is characterized by a viscosity ofno more than 30 centipoise measured using a BROOKFIELD viscometer at aspeed of 60 rpm and a temperature of 25° C.
 2. A water-solubleglyoxalated-polyvinylamide thermosetting resin obtained by the methodaccording to claim
 1. 3. The method according to claim 1 wherein thecellulose reactive agent comprises more than one aldehyde functionality.4. The method according to claim 1, wherein the cellulose reactive agentis glyoxal, glutaraldehyde, furan dialdehyde, 2-hydroxyadipaldehyde,succinaldehyde, dialdehyde starch, diepoxy compounds, and combinationsthereof.
 5. The method according to claim 1 wherein the vinylamidepolymer is a homopolymer or copolymer formed from (meth)acrylamide or asubstituted (meth)acrylamide.
 6. A method according to claim 1 whereinthe vinylamide polymer is nonionic, cationic, potentially cationic,anionic, potentially anionic and/or amphoteric.
 7. The method accordingto claim 6, wherein the vinylamide polymer is cationic and formed from(meth)acrylamide or a substituted (meth)acrylamide and a cationicmonomer, which cationic monomer is selected from the group consisting ofdiallyldialkyl ammonium salts, (dialkylamino)alkyl (meth)acrylates acidaddition or quaternary salts, 2-vinylpyridines acid addition orquaternary salts, dialkylamino alkyl(meth)acrylamides acid addition orquaternary salts, (p-vinylphenyl)-trimethylammonium chloride and1-methacryloyl-4-methyl piperazine acid addition or quaternary ammoniumsalts.
 8. The method according to claim 7, wherein the vinylamidepolymer is formed from about 20 to about 99 weight percent of the(meth)acrylamide or a substituted (meth)acrylamide monomer.
 9. Themethod according to claim 1 wherein the vinylamide polymer or thepolyvinylamide adduct is linear, crosslinked, chain-transferred, orcrosslinked and chain-transferred.
 10. The method according to claim 9,wherein the vinylamide polymer or the polyvinylamide adduct iscrosslinked using at least a difunctional monomer selected from groupconsisting of methylene bis(meth)acrylamide; triallylammonium chloride;tetraallyl ammonium chloride; polyethyleneglycol diacrylate;polyethyleneglycol dimethacrylate; N-vinyl acrylamide; divinylbenzene;tetra(ethyleneglycol) diacrylate; dimethylallylaminoethylacrylateammonium chloride; diallyloxyacetic acid; Na salt; diallyloctylamide;trimethyllpropane ethoxylate triacryalte; N-allylacrylamide;N-methylallylacrylamide; pentaerythritol triacrylate and combinationsthereof.
 11. The method according to claim 1 wherein the vinylamide ispartially hydrolysed or partially converted to a Mannich base.
 12. Themethod according to claim 1 wherein the vinylamide polymer is acopolymer of (meth)acrylamide and diallyldimethylammonium halide. 13.The method according to claim 1 wherein the glyoxal may be added beforethe reaction is catalyzed or added as two or more separate additionsbefore, during, or after the catalyzed reaction.
 14. The methodaccording to claim 1 wherein the reaction is run continuously or inbatch mode.
 15. The method according to claim 1 wherein the averagemolecular weight of the vinylamide polymer is from 500 to about5,000,000.
 16. The method according to claim 1 wherein adduct formationis determined by measuring a change in turbidity or viscosity of theaqueous reaction and the change in turbidity or viscosity is thedifference in turbidity or viscosity of the aqueous reaction at thestart of the reaction and a predetermined endpoint.
 17. The methodaccording to claim 1 wherein the vinylamide concentration is less thanabout 4 weight percent of the total reaction mixture, and the weightaverage molecular weight of the starting vinylamide polymer is between1,000 and 30,000.
 18. The method according to claim 1, wherein thenon-gelled cellulose reactive functionalized polyvinylamide adduct ischaracterized by a turbidity of 2 to 1005 NTU (nephelometric units). 19.The method according to claim 1, wherein the vinylamide polymer has anaverage molecular weight of at least about 30,000 to about 500,000.